You have 10 seconds to name an artist who was active in both the 1960s and 1970s but was better in the 1970s.
Protip: You can't.
Impossible Mode: No David Bowie
If you say Pink Floyd you are a bonafide pleb.
Uh.. Because they were basically the fucking jonas brothers in the sixtees.. Then the Beatles discovered drugs, and went on to actually influence music in a positive way. Answer satisfies op's question.
+hundreds of other art music composers.
They were doing far more interesting things than the bands of the time, just like contemporary composers now are doing the same.
How about Ten Years After, bub? Their shit peaked in the 70's.